The invention relates to an internal combustion engine, in particular a gas engine, for a motor vehicle and to a method for operating an internal combustion engine.
It is generally known to use a cooled and regulated exhaust gas recirculation means (EGR) in order to improve the degree of efficiency of an internal combustion engine, in particular a gas engine. As an addition of inert gas to the gas mixture, the recirculated exhaust gas counteracts a tendency to knock, with the result that an increase in the compression ratio and therefore an improvement in the degree of efficiency are possible in this way. In addition, an increase in the degree of efficiency in the part load range and weak load range takes place by way of a reduction in the gas exchange losses if an exhaust gas recirculation means is used.
For the operation of an internal combustion engine, fuel is metered into the associated air mass flow in a manner known per se depending on the performance requirement. A determination of the respective air mass flow which is as accurate as possible is necessary for predefined metering in of fuel:
In internal combustion engines without an exhaust gas recirculation means, it is known to determine the air mass flow by way of measurement of the manifold absolute pressure (MAP) according to an intake manifold pressure. Here, the cylinder filling is calculated via a model which reproduces the capacity of the engine depending on the rotational speed (volumetric efficiency model). In turn, the air mass flow of the entire engine is calculated from the cylinder filling, with the engine rotational speed being taken into consideration. However, this procedure is not possible in internal combustion engines with an exhaust gas recirculation means, in particular in gas engines with an exhaust gas recirculation means, since said exhaust gas recirculation means is not taken into consideration in the above calculation.
A determination of the air mass flow is also already known which is used in internal combustion engines, in particular in gas engines with an exhaust gas recirculation means (EGR). Here, the air mass flow in the air mass flow feed is measured directly with the aid of a special air mass flow rate meter before the fuel is mixed in and before the recirculated exhaust gas is mixed in. A hot-film air mass flow rate meter (HFM) is known for this purpose. A hot-film air mass flow rate meter of this type is expensive and can be susceptible to faults. In particular, an HFM has proven to be very susceptible to faults in natural gas engines designed to meet the Euro 5 standard on account of its sensitivity to dirt.